Hydraulic Ram Pumps - Technical Brief - Natural Resources Conservation Service

1. HYDRAULIC RAM PUMPS
Introduction
The hydraulic ram pump, or hydram, concept was first developed by the Mongolfier brothers in
France in 1796 (they are better remembered for their pioneering work with hot-air balloons).
Essentially, a hydram is an automatic pumping device which utilises a small fall of water to lift
a fraction of the supply flow to a much greater height; ie it uses a larger flow of water falling
through a small head to lift a small flow of water through a higher head. The main virtue of the
hydram is that its only moving parts are two valves, and it is therefore mechanically very
simple. This gives it very high reliability, minimal maintenance requirements and a long
operation life.
How a hydram works
Its mode of operation depends on the use of the phenomenon called water hammer and the
overall efficiency can be quite good under favourable circumstances. More than 50% of the
energy of the driving flow can be transferred to the delivery flow.
Figure 1 illustrates the principle; initially the impulse valve (or waste valve since it is the non-
pumped water exit) will be open under gravity (or in some designs it is held open by a light
spring) and water will therefore flow down the drive pipe (through a strainer) from the water
source. As the flow accelerates, the hydraulic pressure under the impulse valve and the static
pressure in the body of the hydram will increase until the resulting forces overcome the weight
of the impulse valve and start to close it. As soon as the valve aperture decreases, the water
pressure in the hydram body builds up rapidly and slams the impulse valve shut. The moving
column of water in the drive pipe is no longer able to exit via the impulse valve so its velocity
must suddenly decrease; this continues to cause a considerable rise of pressure which forces
open the delivery valve to the air-chamber.
Once the pressure exceeds the static delivery head, water will be forced up the delivery pipe.
Air trapped in the air chamber is simultaneously compressed to a pressure exceeding the
delivery pressure. Eventually the column of water in the drive pipe comes to a halt and the
static pressure in the casing then falls to near the supply head pressure. The delivery valve will
then close, when the pressure in the air chamber exceeds that in the casing. Water will
continue to be delivered after the delivery valve has

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closed until the compressed air in the air chamber has expanded to a pressure equal to the
delivery head. A check valve is included in the delivery pipe to prevent return flow. When the
delivery valve closes, the reduced pressure in the hydram body will allow the impulse valve to
drop under its own weight, thereby letting the cycle start all over again. Most hydrams operate
at 30-100 cycles a minute.
Figure 1: The hydraulic ram pump principle
The air chamber is a vital component, as apart from improving the efficiency of the process by
allowing delivery to continue after the delivery valve has closed, it is also essential to cushion
the shocks that would otherwise occur due to the incompressible nature of water. If the air
chamber fills with water completely, not only does performance suffer, but the hydram body,
the drive pipe or the air chamber itself can be fractured by the resulting water hammer. Since
water can dissolve air, especially under pressure, there is a tendency for the air in the chamber
to be depleted by being carried away with the delivery flow. Different hydram designs overcome
this problem in different ways. The simplest solution requires the user to stop the hydram
occasionally and drain the air chamber by opening two taps, one to admit air and the other to
release water. Another method on more sophisticated hydrams is to include a so-called
snifting valve which automatically allows air to be drawn into the base of the air chamber when
the water pressure momentarily drops below atmospheric pressure. It is important with such
units to make an occasional check to see that the snifting valve has not become clogged with
dirt and is working properly.
Figure 2: The hydraulic ram pump system

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This cycling of the hydram is timed by the characteristic of the waste valve. Normally it can be
weighted or pre-tensioned by an adjustable spring, and an adjustable screwed stop is generally
provided which will allow the maximum opening to be varied. The efficiency, which dictates
how much water will be delivered from a given drive flow, is critically influenced by the valve
setting.
This is because if the waste valve stays open too long, a smaller proportion of the throughput
water is pumped, so the efficiency is reduced, but if it closes too readily, then the pressure will
not build up for long enough in the hydram body, so again less water will be delivered. There is
often an adjustable bolt which limits the opening of the valve to a predetermined amount which
allows the device to be turned to optimise its performance. A skilled installer should be able to
adjust the waste valve on site to obtain optimum performance. Therefore, it can be seen that
the output of a hydram will be constant and is non-adjustable. A storage tank is usually
included at the top of the delivery pipe to allow water to be drawn in variable amounts as
needed.
Installation requirements
Figure 2 illustrates a typical hydram installation, pumping water to a small storage tank on a
plateau. It can be seen that the supply head is created in this case by creating a weir. In
some cases a small stream is diverted to provide the water supply.
Where greater capacity is needed, it is common practice to install several hydrams in parallel.
This allows a choice of how many to operate at any one time so it can cater for variable supply
flows or variable demand. The size and length of the drive pipe must be in proportion to the
working head from which the ram operates. Also, the drive pipe carries severe internal shock
loads due to water hammer, and therefore normally should be constructed from good quality
steel water pipe. Normally the length of the drive pipe should be around three to seven times
the supply head. Ideally the drive pipe should have a length of at least 100 times its own
diameter. The drive pipe must generally be straight; any bends will not only cause losses of
efficiency, but will result in strong fluctuating sideways forces on the pipe which can cause it to
break loose.
The hydram body requires to be firmly bolted to a concrete foundation, as the beats of its
action apply a significant shock load. The hydram should be located so that the waste valve is
always located above flood water level, as the device will cease to function if the waste valve
becomes submerged. The delivery pipe can be made from any material capable of carrying the
pressure of water leading to the delivery tank. In all except very high head applications, plastic
pipe can be considered; with high heads, the lower end of the delivery line might be better as
steel pipe. The diameter of the delivery line needs to allow for avoiding excessive pipe friction
in relation to the flow rates envisaged and the distance the water is to be conveyed. It is
recommended that a hand-valve or check-valve (non-return valve) should be fitted in the delivery
line near the outlet from the hydram, so that the delivery line does not have to be drained if the
hydram is stopped for adjustment or any other reason. This will also minimise any back flow
past the delivery valve in the air chamber and improve efficiency.
Choice of hydram design
Traditional hydram designs, such as in Figure 3, developed a century ago in Europe, are
extremely robust. They tend to be made from heavy castings and have been known to function
reliably for 50 years or more. However, although a number of such designs are still
manufactured in Europe and the USA in small numbers, they are relatively expensive, although
generally speaking the drive-pipe, delivery pipe and civil workings will be significantly more
expensive than even the heaviest types of hydram.

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Lighter designs, fabricated
using a welded sheet steel
construction, were developed
first in Japan and are now in
production in other parts of
SE Asia including Taiwan
and Thailand. These are
cheaper, but only likely to
last a decade or so as they
are made from thinner
material which will eventually
corrode. Nevertheless they
offer good value for money
and are likely to perform
reliably.
Hydrams are mostly
intended for water supply
duties, in hilly or
mountainous areas,
requiring small flow rates
delivered to high heads. They are less commonly used for irrigation purposes, where the higher
flow rates required will usually demand the use of larger sizes of hydram having 6-inch or 4-inch
drive pipes. Manufacturers usually describe the size of a hydram by the supply and delivery
pipe diameters (generally given in inches even in metric countries because of the common use
of inch sizes for pipe diameters); eg a 6 x 3 hydram has a 6-inch diameter drive pipe and a 3-
inch diameter delivery pipe.
Some simple designs that
can be improvised from pipe
fittings have also been
developed by aid agencies
(Figure 4), and some
interesting versions have also
been quite crudely
improvised using scrap
materials, such as a unit
which is being produced in
some numbers in southern
Laos from materials salvaged
from bombed bridges and
using old propane cylinders
for the air chamber.
Needless to say, such
devices are very low in cost
but the pipes in the end cost
considerably more than the
hydram. They are not always as reliable as traditional designs, but are usually acceptably
reliable with failures separated by many months rather than days, and are easy to repair when
they fail.
Figure 3: Traditional hydram design
Figure 4: A ram pump made from standard pipe fittings

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Performance characteristics
Table 1 indicates estimated performance for typical 4-inch x 2-inch and 6-inch x 3-inch
commercial hydrams.
Hydram size in
inches
4" X 2" 6" X 3"
Head Ratio 5 10 15 20 5 10 15 20
Driven flow
(litres/sec)
8.96 9.7 10 9.02 20.2 17.2 17.1 19.3
Delivery (m³/day) 94 51 35 23 216 101 69 50
Table 1: Estimated performance of hydrams
Costs
The costs of commercial hydrams are typically in the range from about £1500 for small 2-inch
drive pipe sizes up to as much as £5000 for 4-inch or 6-inch sizes. The cost of the drive pipe
can also be quite high for the larger sizes. Therefore hydrams are best suited to relatively low
flow rates and high head applications.
Of course there are no fuel costs and negligible maintenance costs associated with hydrams.
Further information
References
• Jeffery, T D, Thomas T H, Smith A V, Glover, P B, Fountain P D 'Hydraulic Ram Pumps: A
guide to ram pump water supply systems' – ITDG Publishing, 1992
• Iversen H W 'An Analysis of the Hydraulic Ram' - Journal of Fluids Engineering,
Transactions of the American Society of Mechanical Engineers - June 1975.
• Kindel E W 'A Hydraulic Ram for Village Use' - Volunteers in Technical Assistance,
Arlington, VA, USA - 1970 and 1975.
• Hofkes and Visscher 'Renewable Energy Sources for Rural Water Supply in Developing
Countries' - International Reference Centre for Community Water Supply and Sanitation,
The Hague, The Netherlands - 1986.
• Watt S B 'A Manual on the Hydraulic Ram for Pumping Water' - ITDG Publishing, 1975.
Suppliers
Note: This is a selective list of supplies and does not imply ITDG endorsement.
Green and Carter Rams
Vulcan Works
Ashbrittle
Wellington
Somerset
TA21 0LQ.
United Kingdom
Tel: +44 (0)1823 672365
John Blake Ltd.
P.O.Box 43
Royal Works
Atlas Street
Clayton Le Moors
Lancashire, BB5 5LP
United Kingdom
Tel: 01254 235441
Fax: 01254 382899
E-mail: sales@allspeeds.co.uk

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Website: www.allspeeds.co.uk
Useful Addresses
Development Technology Unit (DTU)
School of Engineering
University of Warwick
Coventry CV4 7AL
United Kingdom
Tel: +44 (0)1203 522339
Fax: +44 (0)1203 418922
E-mail: dgr@eng.warwick.ac.uk
Website: http://www.eng.warwick.ac.uk/DTU
Development Technology Unit who has carried out a lot of research into simplifying the
construction of hydraulic ram pumps. The DTU is a research unit within the School of
Engineering at the University of Warwick in the UK. The aim of the DTU is to research and
promote appropriate technologies for application in Developing Countries.
WOT - Werkgroep Ontwikkelingstechnieken
Working Group on Development Techniques
Vrijhof 205/206
P.O.Box 217
7500 AE Enschede
The Netherlands
Tel: +31 53 489 3845
Fax: +31 53 489 2671
E-mail: wot@tdg.utwente.nl
http://www.student.utwentw.nl/~wot/
WOT is a non-profit organisation working in the field of small scale sustainable energy, based
at the University of Twente.